Marine Auxiliary Machinery This page intentionally left blank Marine Auxiliary Machinery Seventh edition H D McGeorge C Eng, FIMarE, MRINA, MPhil OXFORD AMSTERDAM BOSTON LONDON NEW YORK PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO Butterworth-Heinemann An imprint of Elsevier Science Linacre House, Jordan Hill, Oxford OX2 8DP 225 Wild wood Avenue, Woburn, MA 01801-2041 First published 1952 Second edition 1955 Third edition 1963 Fourth edition 1968 Reprinted 1971,1973 Fifth edition 1975 Reprinted 1976,1979 Sixth edition 1983 Reprinted 1987 Seventh edition 1995 Paperback edition 1998 Reprinted 1999, 2000 (twice), 2002 © Copyright 1995, Elsevier Science Ltd All rights reserved No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidental! to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England WIT 4LP Applications for the copyright holder's written permission to reproduce any part of this publication should be addressed tit the publishers British Library Cataloguing in Publication Data Marine Auxiliary Machinery - 7lh rev edn I McGeorge, H David 0623.8 Library of Congress Cataloguing in Publication Data McCeorge, H D Marine Auxiliary Machinery/H D McGeorge - 7th edn Includes bibliographical references and index Marine engines Marine machinery I Title VM765.M38 1995 623.8'6—dc20 95-3360 CIP ISBN 7506 4398 For more information on all Butterworth-Heinemann publications please visit our website at www.bh.com Typeset by Vision Typesetting, Manchester Printed and bound in Great Britain by MPG Books Ltd, Bodrnin, Cornwall Contents Preface Acknowledgements vil ix Main propulsion services and heat exchangers Machinery service systems and equipment 40 Ship service systems 78 Valves and pipelines 112 Pumps and pumping 139 Tanker and gas carrier cargo pumps and systems 176 Auxiliary power 214 The propeller shaft 245 Steering gears 286 10 Bow thrasters, stabilizers and stabilizing systems 314 11 Refrigeration 333 12 Heating, ventilation and air conditioning 368 13 Deck machinery and cargo equipment 392 14 Fire protection 418 15 Safety and safety equipment 458 16 Control and instrumentation 480 Index 507 This page intentionally left blank Preface The preparation of the seventh edition of this established book on marine auxiliary machinery has necessitated the removal of some old material and the inclusion of new topics to make it relevant to the present day certificate of competency examinations It is hoped that the line drawings, many of which were provided by Mr R C Dean, a former colleague in London, will be useful for the certificate of competency and other examinations The majority of other illustrations and much of the basic text have been provided over the years by the various firms listed in the Acknowledgements I am grateful to those firms who have supplied me with material added in this edition H D McGeorge This page intentionally left blank Acknowledgements The author and publishers would like to acknowledge the cooperation of the following who have assisted in the preparation of the book by supplying information and illustrations, Alfa-Laval Ltd APE-Allen Ltd ASEA, Auto-Klean Strainers Ltd Bell & Howell Cons Electrodynamics Blakeborough & Sons Ltd Blohm & Voss A.G Brown Bros & Co Ltd B.S.R.A Bureau Veritas Caird & Rayner Ltd Caterpillar Traction Co Chubb Fire Security Ltd Clarke, Chapman Ltd Cockburn-Rockwell Ltd Crane Packing W Crockatt & Sons Ltd R C Dean Deep Sea Seals Ltd The Distillers Co Ltd (CO2 Div.) Donkin & Co Ltd Fire Fighting Enterprises Ltd Fisher Control Valves Ltd G & M Firkins Ltd Foxboro-Yoxall Ltd G.E.C.-Elliott Control Valves Ltd Germannischer Lloyd Glacier Metal Ltd Hall Thermotank Ltd The Henri Kummerman Foundation Howden Godfrey Ltd Hamworthy Engineering Ltd Harland & Wolff Ltd John Hastie & Co Ltd Hattersley Newman Hender Ltd Hawthorn Leslie (Engineers) Ltd Hindle Cockburns Ltd James Howden & Co Ltd F A Hughes & Co Ltd W C Holmes & Co Ltd Howaldtswerke-Deutche Werft A.G Hydraulics & Pneumatics Ltd IMI-Bailey Valves Ltd IMO Industri International Maritime Organisation KaMeWa Richard Klinger Ltd Kockums (Sweden) K.D.G Instruments Ltd Lister Blackstone Mirrlees Marine Ltd Lloyds Register of Shipping Mather & Platt Ltd Metering Pumps Ltd Michell Bearings Ltd Nash Engineering (G.B.) Ltd Navire Cargo Gear Int AB Norwinch Peabody Ltd Penwalt Ltd Peter Brotherhood Ltd Petters Ltd Phillips Electrical Ltd Thos Reid & Sons (Paisley) Ltd Ross-Turnbull Ltd Royles Ltd Ruston Paxman Diesels Ltd Simplex-Turbulo Marine Ltd Serck Heat Exchangers Ltd Spirax-Sarco Ltd Sofrance Sperry Marine Systems Ltd Stella-Meta Filters Ltd Stone Manganese Marine Ltd Stothert & Pitt Ltd Svanehoj, Denmark Taylor Servomax United Filters & Engineering Ltd Vickers Ltd Vokes Ltd Vosper Ltd The Walter Kidde Co Ltd Weir Pumps Ltd Welin Davit & Engineering Ltd Wilson-Elsan Ltd Worthington-Simpson Ltd Main propulsion services and heat exchangers 15 Figure 1.10 Central cooling system evaporator, the cooling water is led back to the suction of the high temperature pump through a control valve (C) which is governed by engine inlet temperature The control valve mixes the low and high temperature streams to produce the required inlet temperature, which is about 62°C Engine outlet temperature may be about 70°C For the low temperature circuit, the heat of the water leaving the central coolers is regulated by the control valve (F) Components of the system are arranged in parallel or series groups as required The pressure control valve works on a bypass The temperature of the water after the cooler may be 35°C and at exit from the main engine lubricating oil coolers it is about 45°C The fresh water in the closed system is treated with chemicals to prevent corrosion of the pipework and coolers With correct chemical treatment, corrosion is eliminated in the fresh water system, without the need for expensive materials 16 Main propulsion services and heat exchangers Figure 1.11 Scoop arrangement for motorship central cooling system Scoop arrangement for a motor ship A scoop (Figure 1.11) designed to supply sea-water circulation through the central coolers while the vessel is underway, may be installed instead of a conventional sea-water circulating pump The scoop imposes some extra drag on the hull so that the power for sea-water circulation is supplied from the main propulsion instead of from the generators and electrical system Economic advantages are claimed for a correctly designed scoop but the arrangement is viable only for a simple straight through flow as for central coolers or the large condenser of a steam ship The electrically driven pump is used only for manoeuvring or slow speeds It is of smaller capacity than would be required for an ordinary circulating pump Circulating systems for steamships The main sea-water circulating system for a ship with main propulsion by steam turbine is similar to that of a motorship with a central cooling system The difference is that the sea water passes through a large condenser and an oil cooler rather than central coolers and then to the overboard discharge The main sea-water inlets, port and starboard, may be arranged as for the motorship example (Figure 1.1) with high and low suctions, orthodox double entry circulating pump (with emergency bilge suction) and a stand-by pump Alternatively, the arrangement may be based on a scoop to supply the main Main propulsion services and heat exchangers 17 condenser Scoops have been preferred for fast, high-powered steamships, with circulation only through a single large condenser and sufficient speed to ensure that the scoop gives an adequate flow of water Small axial flow circulating pumps (Figure 1.12) have been installed in conjunction with some scoop arrangements, with the idea that at speed, the pump impeller would idle and provide very little resistance to the scoop flow The axial flow pump, intended for slow speed and manoeuvring, suffered from thrust problems when idling in a number of installations Closed feed system and feed heating To ensure trouble-free operation of water-tube boilers the feed water must be of high quality with a minimal solid content and an absence of dissolved gases Solids are deposited on the inside surfaces of steam generating tubes, as the water boils off, and the scale so formed causes overheating and failure Dissolved gases tend to promote corrosion Distilled water used as boiler feed has a great affinity for gases in the atmosphere Chemical treatment is aimed at preventing corrosion problems but the boiler closed feed system must play its part in maintaining minimal contact between feed water and air at every stage and in promoting the dissociation and removal of any air or other gases The feed system also assists efficient operation by condensing used steam and returning it to the boiler as feed at the highest temperature attainable economically In practical terms, this means maximum recovery of the latent Figure 1.12 Scoop system for steamship with axial flow pump 18 Main propulsion services and heat exchangers heat in steam Regenerative condensers and de-aerators are two major components in the complex feed systems which have been evolved The feed system for a tanker (Figure 1.13) shows a superheated steam supply from two water-tube boilers to the main propulsion turbine, the turbo-alternator and for cargo pumps Each of these is served by a separate condenser and extraction pumps which return condensate to the closed feed system The condenser A condenser is a vessel in which a vapour is deprived of its latent heat of vaporization and so is changed to its liquid state, usually by cooling at constant pressure In surface condensers, steam enters at an upper level, passes over tubes in which cold sea water circulates, falls as water to the bottom and is removed by a pump (or flows to a feed tank) The construction of condensers is similar to that of other tubular heat exchangers, with size variation extending up to the very large regenerative condensers for main propulsion steam turbines Some smaller condensers may have U tubes for a two-pass flow and free expansion and contraction of tubes The cooling water for straight tube condensers, circulates in one or two passes, entering at the bottom With a scoop, there is one pass flow A water box, of cast iron or steel, is fitted at each end (one end with U tubes) of the shell Sandwiched between the flanges of the boxes and the shell are admiralty brass (70% Cu, 29% Zn, 1% Sn) tube plates These are drilled and when soft-packing is used, counter bored and tapped Tubes may be of cupro-nickel (70% Cu, 30% Ni) or aluminium brass (76% Cu, 22% Zn, 2% Al) and of 16-20 mm outside diameter Straight tubes can be expanded into the tube plates at both ends (Figure 1.3), expanded at the outlet end and fitted with soft packing at the other, or fitted with soft packing at both ends (Figure 1.14) An expansion allowance (Figure 1.15), provided where tubes are expanded into tube plates at both ends, may take the form of a shell expansion joint Tubes are prevented from sagging by a number of mild steel tube support plates A baffle plate at the entrance to the steam space, prevents damage from the direct impact of steam on the tubes Access doors are provided in the water box end covers of very large condensers for routine inspection and cleaning, with one or more manholes in the shell bottom for the same purpose Corrosion by galvanic action is inhibited by zinc or mild steel sacrificial anodes or alternatively, impressed current protection may be used Dezincification of brasses may be prevented by additives, such as 0.04% arsenic, to the alloy Tube failure is likely to be caused by impingement, that is corrosion/erosion arising from entrained air in, or excessive speed of, circulating water Failure could otherwise be from stress/corrosion cracking or dezincification of brass tubes Defective tubes can be plugged temporarily Figure 1.13 Closed feed system for a tanker (Weir Pumps Ltd) 20 Main propulsion services and heat exchangers Figure 1.14 Example of safe packing assembly for condenser tubes (courtesy of Crane Packing) Figure 1.15 Shell expansion joint The regenerative condenser As it expands through a turbine, as much as possible of the available useful work is extracted from the steam by maintaining vacuum conditions in the condenser Part of the function of the condenser is to condense the steam from the low pressure end of the turbine at as low a pressure as possible The effective operation of a condenser requires that the sea water is colder than the saturation temperature of the exhaust steam and this means that undercooling will occur Any undercooling must be made good during the cycle which turns the feed water back to steam, and undercooling increases the temperature range through which the condensate, returning to the boiler, must be raised again before it boils off To avoid this thermal loss, condensers are built with regenerative ability in that paths (Figure 1.16) are arranged between and below the tube banks for direct flow of part of the steam to the lower part of the condenser This steam then flows up between the tubes and meets the condensate from the main part of the exhaust, dripping from the tubes The undercooled condensate falls through this steam atmosphere and heat transfer occurs, resulting in negligible undercooling in the final condensate Main propulsion services and heat exchangers 21 Figure 1.16 Weir's regenerative condenser (courtesy G & J Weir Ltd, Glasgow) The condensate, dripping from the tubes, may be below the saturation temperature corresponding to the vacuum, by as much as 5°C, initially The de-aeration performance of a condenser is also related to undercooling in that the amount of gas, such as oxygen, that can remain in solution in a water droplet at below saturation temperature is dependent on the degree of undercooling Theoretically, if a water droplet is at the saturation temperature then no gas will remain in solution with it One method of reducing the degree of undercooling when sea water temperature is low, is to recirculate a portion of the cooling water to enable the condenser to be worked at its design condition, whenever possible The feed system and feed heating Non-condensable gases and some vapour are removed from the main condenser (Figure 1.13) by an air ejector, cooled by the main condensate and released in the ejector condenser The condensed ejector steam passes with other clean drains (gland stearn condenser, low pressure feed heater, evaporator) to a drains tank from which a pump draws, to discharge, with the mains condensate, to the de-aerator It is common practice to reflux these drains, that is to return them to the main condenser in the form of a spray at a high level where, meeting the turbine exhaust, they are de-aerated before mixing with the main body of the condensate and being removed by the condensate extraction pump Heating steam for the steam/steam generator, the de-aerator and the low pressure feed heater are bled from the main turbines at appropriate stages, so 22 Main propulsion services and heat exchangers that all of the latent heat Is recovered The feed pump exhaust is treated similarly The steam/steam generator, providing low pressure steam for services whose condensate may be contaminated, has its own separate feed system The centrifugal extraction pump, driven either by electric motor or steam turbine, draws from the condenser and delivers to a de-aerating heater through the heat exchangers already mentioned Another extraction pump passes the de-aerated feed to a multi-stage centrifugal pump, also either electric motor or, more often, turbine driven The pump delivers the feed to the boilers at a temperature approaching that of saturation through a high pressure feed heater, supplied with steam bled from the high pressure turbine Make-up feed is produced by evaporation and distillation (sometimes double) at subatmospheric pressure, stored in a tank and introduced to the boilers from the main condenser with the refluxed drains or through the de-aerator The feed pumps, feed piping and fittings are duplicated Steam-jet air ejector A steam-jet ejector may be used to withdraw air and dissolved gases from the condenser In each stage of the steam-jet ejector, high pressure steam is expanded in a convergent/divergent nozzle The steam leaves the nozzle at a very high velocity in the order of 1220 m/s and a proportion of the kinetic energy in the steam jet transferred, by interchange of momentum, to the body of air which is entrained and passes along with the operating steam through a diffuser in which the kinetic energy of the combined stream is re-converted to pressure energy The maximum pressure ratio that can be obtained with a single stage is roughly 5:1 and consequently it is necessary to use two or even three stages in series, to establish a vacuum in the order of 724 mm Hg, with reasonable steam consumption There are a variety of ejector designs in service which work on the same principle Older units have heavy cast steel shells which serve as vapour condensers and also contain the difrusers These are arranged vertically, the steam entering at the top (Figure 1.17) More recent designs have the difrusers arranged externally and the vapour condenser shell is somewhat lighter in construction Horizontal and vertical arrangements can be found and some units are arranged as combined air ejectors and gland steam condensers Horizontal single element two stage air ejector An air ejector which has been commonly used, is shown schematically in Figure 1.18 The unit comprises a stack of U-tubes contained in a fabricated mild steel condenser shell on which is mounted a single element two stage air ejector The condensate from the main or auxiliary condenser is used as the cooling medium, the condensate circulating through the tubes whilst the air and vapour passes through the shell The high velocity operating steam emerging from the first stage ejector nozzle entrains the non-condensables and vapour from the Main propulsion services and heat exchangers Figure 1.17 23 Three stage air ejector with internal diffusers main condenser and the mixture discharges into the inter (or first stage) condenser Most of the steam and vapour is condensed when it comes into contact with the cool surface of the tubes, falls to the bottom of the shell and drains to the main or auxiliary condenser The remaining air and water vapour are drawn into the second stage ejector and discharged to the after (or second stage) condenser The condensate then passes to the steam drains tank and the non-condensables are discharged to the atmosphere through a vacuum retaining valve 24 Main propulsion services and heat exchangers Figure 1.18 Horizontal single element two stage air ejector The vacuum retaining valve is shown in Figure 1,19 which is fitted as a safety device to reduce the rate of loss of vacuum in the main condenser if the air ejector fails It is mounted on a pocket built out from the second stage condenser, and consists essentially of a light stainless steel annular valve plate which covers ports in a gunmetal valve seat When the pressure inside the after condenser exceeds atmospheric pressure the valve lifts and allows the gases to escape to atmosphere A relief valve is fitted on the first stage condenser shell of the twin element unit The ejector stages, Figure 1.20, consist of monel metal nozzles in mild steel holders discharging into gunmetal difrusers Expansion is allowed for by sliding feet at the inlet end Nash rotary liquid ring pumps Nash rotary liquid ring pumps, in association with atmospheric air ejectors, may be used instead of diffuser-type steam ejectors and are arranged as shown in Figure 1.21 The pump, discharging to a separator, draws from the condenser Figure 1.19 Vacuum retaining valve Main propulsion services and heat exchangers 25 Figure 1.20 Figure 1.21 First and second stage ejectors Nash liquid pump ring through the atmospheric air ejector, creating a partial vacuum of about 600 mm Hg At this stage the ejector, taking its operating air from the discharge separator, which is vented to atmosphere, comes into action, sonic velocity is attained and vacua in the order of 725 mm Hg maintained in the condenser The liquid ring pump is sealed with fresh water recycled through a sea-water cooled heat exchanger The Nash pump, using recycled fresh water for sealing, may be also used to provide oil-free instrument air at a pressure of bar (Figure 1.22) Condensate extraction pump Removal of condensate from a condenser imposes very difficult suction conditions on the pump The available net positive suction head (NPSH) is minimal because the condenser is situated low in the ship permitting a static suction head of only 450—700 mm and the condensate is at, or near its vapour pressure It is necessary therefore to ensure that the pump's required NPSH is correspondingly low and to this end suction passages and inlets are given ample area The purnps used for the duty, are two stage units (Figure 1.23a) the first stage impeller being arranged as low as possible in the pump with an upward facing eye This impeller feeds a second impeller via suitable passages in the pump casing 26 Main propulsion services and heat exchangers Figure 1.22 Using recycled fresh water for sealing (Nash Engineering Co (GB) Ltd) Where extraction pumps are fed from de-aerators or drain coolers, the pump suction level is maintained constant by a specially designed float control In instances where the pump is drawing from the main condenser however, it is common practice to operate the pump on a free suction head This means that the pump must operate with a variable NPSH at varying flow rates Figure 1.23b shows the head/quantity (H/Q) curve for a two stage extraction pump operating under a variable NPSH The system resistance curve is interposed on the diagram When operating at the specified maximum capacity, the flow rate corresponds to that at the intersection of the natural H/Q characteristic of the pump and the system resistance curve As the level of condensate in the suction sump falls below the point where the available NPSH intersects with the minimum required NPSH the pump starts to cavitate and its output is regulated The natural H/Q characteristic is modified as the discharge pressure is reduced to that required to overcome the resistance of the system at the reduced flow rate When the suction level increases the flow rate increases Therefore, inherent control of the flow rate is achieved without the use of a float controlled regulator Such a system is usually referred to as cavitation control The extraction pump is a ca vita ting pump Feed water heaters Surface or direct contact feed heaters, play an important part in the recovery of latent heat from exhaust steam Direct contact feed heaters are also known as de-aerators Surface feed heaters These are shell and tube heat exchangers, made with materials and scantlings appropriate to their working temperatures and pressures It can be shown that the minimum economic terminal difference (i.e the temperature difference Main propulsion services and heat exchangers 27 Figure 1.23 (a) Weir two stage extraction pump Pump casing (split) Pump spindle Impeller (1st stage) Impeller nut and tag washer {1st stage) Casing ring (1st stage) Dowel pins Bottom cover Bottom bush liner Intermediate bush 10 Impeller (2nd stage) 11 Impeller nut and lock screw (2nd stage) 12 Casing ring (2nd stage) 13 Plug 14 Mechanical seal 15 Seal clamping plate 16 Motor stool 17 Thrust bearing housing 18 Thrust bearing cover 19 Thrust bearing end cover 20 Thrust bearing 21 Thrust nut and lock screw 22 'V ring 23 Distance piece 24 Flexible coupling (pump half) 25 Flexible coupling (motor half) 26 Coupling bolt and nut 27 Coupling pad 28 Grease lubricator 29 Water return pipe 30 Water supply pipe 31 Pump feet between the heating fluid inlet and the heated fluid outlet) is about 6°C If, however, the heating fluid (steam) is superheated by at least 110°C above saturation temperature and the heated fluid (feed water) leaves the heater at this saturation temperature or near to it, this terminal difference will be very small or zero This can be achieved by using the exit section of the feed heater as a de-superheater By grouping a number of surface feed heaters in one module, an economy in 28 Main propulsion services and heat exchangers Figure 1.23(b) Extraction pump cavitation control curves space and pipe connections can often be achieved and there is a movement in that direction in practice Many parts of the feed system are now installed as packaged units or modules Figure 1.24 shows a package arrangement which combines no less than four different units, viz steam jet air ejectors, glands steam condenser, the de-aerator vent condenser and the low pressure heater drains cooler Such packaging obviously leads to compactness, centralization and reduction of branches to be connected by the shipbuilder Other 'packaged' feed systems incorporate complete feed systems and Figure 1.25 shows an arrangement of a packaged feed system for a 67000 tonne tanker De-aerators Mention has been made of the need for clean, neutral boiler feed, free from dissolved gases and of the consequent use of efficient de-aerators Figure 1.26 shows one of several which liberate the dissolved gases from the feed and provide a measure of feed heating simultaneously This type of de-aerator has a great range of capacity and given a temperature rise of at least 20°C, an oxygen content of 0.2 cc/litre can be reduced to 0.005 cc/litre, when working between one-half full load and full load in a closed feed system Normally, the de-aerator is mounted directly on a storage tank, into which the de-aerated water falls, to be withdrawn through a bottom connection by a Main propulsion services and heat exchangers 29 Figure 1.24 This module combines four closed feed system components and is claimed to offer a 14% reduction in weight and a 19% reduction in volume Steam jet air ejector, electrically driven vapour extractor, gland steam condenser, LP heater/drains cooler, supporting feet, water heater pump or by gravity The tank usually has a capacity sufficient for 10 minutes' running supply of water but this is not necessarily the case The feed water enters the de-aerator head and so that its surface area may be increased to the maximum possible, it is divided into sprays of minute droplets by being forced through the spray nozzles into the shell; here it meets the heating steam and is brought rapidly to its saturation temperature Most of the dissolved gases are released and with some vapour rise to the vapour release opening The header may be divided and provided with two feed inlet connections, so that the efficiency of de-aeration may be maintained at low rates of flow, by reducing the number of nozzles in use Cascade trays Three cascade trays are set one above the other in the lower part of the shell The upper and lower of these trays have a raised lip on the outer periphery, have the central opening blanked and have a series of perforations arranged in rings towards the raised lip The middle tray has a central opening with a raised lip and is perforated similarly The falling spray collects on the upper tray and is again broken up as it passes through the perforations to the middle tray where the process is repeated, to be repeated again as it passes through the lower tray to the tank below The combination of spray, heating and cascade ensures the liberation of all but a minute fraction of the gases in solution or suspension The final water temperature depends upon the pressure of the controlled steam supply ... published 19 52 Second edition 19 55 Third edition 19 63 Fourth edition 19 68 Reprinted 1 9 71 ,1 973 Fifth edition 1 975 Reprinted 1 976 ,1 979 Sixth edition 19 83 Reprinted 19 87 Seventh edition 19 95 Paperback... been made of the need for clean, neutral boiler feed, free from dissolved gases and of the consequent use of efficient de-aerators Figure 1. 26 shows one of several which liberate the dissolved... feed heating Non-condensable gases and some vapour are removed from the main condenser (Figure 1. 13) by an air ejector, cooled by the main condensate and released in the ejector condenser The